1. Field of the Invention
The present invention relates to a linear guide device used, for example, in a linear motion component of a machine tool or an industrial robot.
2. Description of the Related Art
A linear guide device of a type described above has been disclosed in Japanese Laid-Open Patent publication No. 62-200016. Specifically, as shown in FIG. 17, a bearing block (a) (which will be called merely a "block") is provided at its opposite side surfaces with load ball grooves (c) in which balls (b) rolls. A pair of track beds (d) is disposed with the block (a) therebetween. The beds (d) are provided with ball rolling grooves opposed to the load ball grooves (c). The balls (b) held between the load ball grooves (c) and the ball rolling grooves support the block (a) so that the block (a) may be movable along the track beds (d).
A screw shaft (f) of a feed screw mechanism is engaged with a central portion of the block (a), so that the screw shaft (f) may be rotated to move the block (a) along the track beds (d).
According to this linear guide device, since the bearing block for supporting a movable member such as the table is constructed integrally with the feed screw mechanism for applying a driving force for the linea motion to the movable member, a compact construction of the device can be achieved, and a height of the movable member can be minimized, which enables a stable motion.
However, with respect to the bearing block of the linear guide device described above, opposite ends of each load ball groove must be connected by a ball circulation path so as to guide or introduce the balls from a termination end of the load ball groove to a start end of the load ball groove again.
In the prior art, the ball circulation path is generally formed of a no-load ball rolling aperture, which is formed in the block to correspond to each load ball groove, and ball return paths, each of which connects an end of the ball load groove and an end of the no-load ball rolling aperture.
However, the no-load ball rolling aperture is a very small aperture having a diameter only slightly larger than that of the ball, and thus it is difficult to form a long no-load ball rolling aperture by drilling. Therefore, machining of the no-load rolling aperture restricts increase of a length of the block, and thus restricts the length of the load ball groove.
Generally, in a bearing which employs rolling members such as balls for bearing the motion between two objects, a maximum allowable load may be increased by 1 increasing sizes of the rolling members, or 2 increasing numbers of the rolling members which rolls on the load rolling groove. However, the latter can be hardly applied to practical products because the lengths of the load ball grooves are restricted due to the above described reason.
The present invention is devised in view of the above problems. It is an object of the invention to provide a linear guide devide, which allows easy formation of no-load rolling apertures for rolling members and has a large maximum allowable load and a small sizes.